β-Mannans such as glucomannan and galactomannan are compounds having 1,4-β-D-mannoside bond and are widely present in the natural world as a component of hemicellulose, which is one of main components of plant cell walls. This 1,4-β-D-mannoside bond is hydrolyzed by β-1,4-mannanase (EC3.2.1.78) or β-mannosidase (EC3.2.1.25). α-1,6-galactoside bond present in galactomannan is hydrolyzed by α-galactosidase (EC3.2.1.22). Acetylated β-mannans are deacetylated by the action of acetylmannan esterase (EC3.1.1.6) (throughout this specification, β-1,4-mannanase, β-mannosidase, α-galactosidase, and acetylmannan esterase are collectively referred to as “mannan hydrolases”). Among these mannan hydrolases, β-1,4-mannanase is an industrially useful enzyme and is widely used in industries such as foods, stockbreeding, and papermaking (throughout this specification, β-1,4-mannanase is referred to as “mannanase”, and β-1,4-mannosidase is referred to as “mannosidase”).
As the mannanases, there are known those derived from Ascomycotina filamentous fungi such as Trichoderma reesei (for example, see NPL 1) and Aspergillus aculeatus (for example, see PTL 1) and those derived from Basidiomycotina filamentous fungi such as Agaricus bisporus (for example, see NPL 2). As the mannanases derived from bacteria (for example, see NPL 3), there are known those derived from, for example, Streptomyces lividans (for example, see NPL 4) and Pseudomonas fluorescens (for example, see NPL 5). Genes of these mannanases have been also reported.
As enzymes that are known but their genes have not been reported, there are known, for example, those derived from Aspergillus tamarii (for example, see NPL 6) and Penicillium multi. color (for example, see PTL 2).
Aspergillus oryzae and Aspergillus sojae, which are yellow koji molds, have been used in production of brewed foods such as soy sauce, miso, and rice wine from ancient times in Japan. These koji molds have high enzyme-producing abilities and high safety credibility based on the longtime use thereof and are therefore industrially important microorganisms. Regarding these yellow koji molds, there are reports on mannanase derived from Aspergillus oryzae (for example, see NPL 7) and also reports on the enzyme after purification and a gene of the enzyme (for example, see PTL 3).
As one of transcription regulatory factors that positively or negatively regulate the expression of genes of the above-mentioned mannanases, in prokaryotes, a negative regulatory factor (reppressor) derived from Bacillus subtilis has been reported (for example, see NPL 8.). However, in eukaryotes including molds, transcription regulatory factors for mannanases have not been found yet. In eukaryotes, not only transcription regulatory factors regulating the expression of genes of mannanases, but also transcription regulatory factors regulating the expression of genes of mannosidase and α-galactosidase, which participate in hydrolysis of mannans, have not been found. Therefore, production of a eukaryotic microorganism strain, the mannan hydrolase-producing capability of which has been enhanced by forced expression of the transcription regulatory factor, has not also been investigated.
In degradation of woody biomass, in addition to mannan hydrolases, the actions of cellulose hydrolases (e.g., a cellulase, cellobiohydrolases, or β-glucanases, or β-glucosidase that degrades oligosaccharides produced by the action of a cellobiohydrolase or a glucanase) are also important. Accordingly, it is expected that production of a large amount of cellulose hydrolases together with mannan hydrolases is effective for efficient production of enzyme preparations of degrading woody biomass. If the transcription regulatory factor positively regulates the expression of genes of both mannan hydrolase and cellulose hydrolase, it is probably possible to breed a eukaryotic microorganism strain of which capability of producing both the hydrolases has been enhanced by forced expression of the transcription regulatory factor. However, such investigation has not been performed to date.